Although fiber-based cigarette filter elements are well known and have been used for a number of years, the choice of components for this class of filters has remained quite limited over the years due to cost factors and lack of general suitability of many natural fibers for high speed filter production using state of the art filter rod-making apparatus. In addition, the demands on present day commercial cigarette filter elements tend to conflict, particularly with respect to general filtration efficiency and increased demand for selective filtration of cigarette smoke components.
While various fibers and fiber mixtures have been tried and evaluated, a substantial number of cigarette filter elements continue to favor old technology because of certain cost and handling advantages. For example, cellulose acetate tow can be readily processed into cuttable filter rods using an essentially unmodified state-of-the art filter rod-making apparatus without serious jamming problems. This advantage is enjoyed despite increased need for substantial amounts of additives, including organic plasticizers such as triacetin, diacetin, citric acid, as well as lubricants, flavors, medicines, selective filtering agents and the like. Generally, such additives are applied as aqueous solutions onto opened fiber tow by art-recognized dipping, spraying, or printing techniques.
The advantages of cellulose acetate fiber as filter substrate, however, are countered by certain disadvantages. For example, such fiber tends to be relatively weak compared with thermoplastic synthetics such as polyolefin fiber or filament. This characteristic seriously limits the amount of tension and crimp that a cellulose acetate fiber tow of low dpf will tolerate prior to introduction into a conventional filter rod-making apparatus.
Synthetics such as polyolefin fiber, however, also have some disadvantages. These arise from the fact that polyolefin substrates are generally hydrophobic and tend to be chemically inert, while a majority of known cigarette filter additives are hydrophilic. For this reason it is sometimes very difficult to apply and retain such additives in proper amount and functional condition within filter elements using hydrophobic synthetic fiber as a major substrate component.
Another problem, unique to the cigarette filter art, concerns the difficulty in optimizing fiber denier and general filter efficiency of synthetic fiber filters without corresponding sacrifice in dimensional stability, hardness, and pressure drop or draw across the filter element.
It is an object of the present invention to obtain cigarette filters of superior efficiency and draw which can be tailored to a wide variety of tobacco mixtures while retaining known advantages of various filter substrates or combinations thereof.
It is a further object of the present invention to control selectively both filter delivery and filter retention of nicotine by-product in cigarette smoke, compared with pass through concentrations of total particulate matter.